An electrodynamic transducer head of this type is disclosed in GB-A-20 06 433. In this case, the electromagnet required consists of two coaxial poles whose end faces directed towards the workpiece to be tested match the geometry of the surface of the workpiece to be tested. An exciting coil and receiving coil, which are covered by a ceramic layer on the workpiece side and by an insulating layer on the magnet pole side, are arranged on the internal pole shoe which also consists of two coaxial portions, on the front face thereof. One of the drawbacks of this design of pole shoes is that feedback from the workpiece to be tested and the resulting eddy currents in the pole shoe prevent the resolution of the test signal from being influenced. Furthermore, it is not possible to place an electrodynamic transducer head of this type in the region of the exciting and receiving coil directly on the workpiece and to take measurements while the electromagnet is rotating and/or while the workpiece is rotating because the surface of the workpiece, which resembles emery paper, would instantly destroy the exciting and receiving coil. In other words, the cover composed of ceramic materials is not resistant to abrasion.
DE-OS 31 23 935 describes an electrodynamic transducer head which also comprises an internal pole of an electromagnet surrounded by an external pole shoe, the internal pole shoe having exciting and receiving coils on its end face and also having radial slits into which transformer plates, insulated if necessary, may be introduced. This arrangement should eliminate feedback from the workpiece into the pole shoe, allowing high resolution of the measured values. However, an electrodynamic transducer head of this type cannot be placed on a workpiece to be tested, in particular on a tube, and cannot be moved relative thereto because this would lead to immediate destruction of the measuring system.